It is generally known to use composite structural panels comprising polymer materials as interior trim components in motor vehicles, aircraft, railroad cars, and the like. Such trim components include molded dashboards, interior door panels and inserts, headliners, and the like. Conventional present-day composite panels for use as such trim components are made of a polyurethane foam material reinforced with glass fibers saturated or embedded in epoxy resin. More specifically, one or more layers of glass rovings impregnated with epoxy resin are laminated onto the foam for reinforcing and stiffening the resulting composite panel. As a further alternative, a polypropylene powder material may be incorporated in the glass roving layers as a binder.
Such a conventional composite panel and the method of its manufacture suffer distinct disadvantages, For example, handling of the glass fiber material and handling and application of the epoxy resin in fluid form are difficult and complicated, especially in view of worker safety and environmental concerns. Moreover, this process, for example carried out as a lay-up process, requires substantial handling effort, and also a long curing time for the hardening the resin in a heated compression mold. Since the finished trim components contain a mixture of different non-degradable and incompatible materials, e.g. polyurethane foam, glass fibers and epoxy resin, these trim components are not recyclable by means of separation and reprocessing of the materials. Since at least some of the materials are non-combustible or give off noxious or toxic gases when combusted, the trim components are also not thermo-recyclable, i.e. burnable as a fuel. The recyclability of composite structural panels in general, and especially motor vehicle trim components, is presently a strong driving force in the industry. There is a great need to provide composite materials that can be easily separated, reprocessed for reuse, or combusted as an industrial fuel.
Another type of known composite structural panel, as disclosed in U.S. Pat. No. 5,709,925 (Spengler et al.) is based on a combination of natural fibers and a fibrous thermoplastic material. More particularly, such a composite structural panel includes a laminated composite substrate that comprises a core layer and two cover layers laminated onto the core layer, wherein the core layer comprises natural fibers and a fibrous thermoplastic material, and each cover layer respectively comprises synthetic fibers and a fibrous thermoplastic material. Such a structural panel achieves environmental advantages, because all of the materials of the multi-layer panel are easily broken down or otherwise processed for reuse or recycling. Namely, all of the materials can be burned without producing toxic gases, or the thermoplastic material can be melted down while burning off the natural fibers and/or separating out the fiber materials. These known structural panels also achieve very good impact energy absorption without splintering or shattering, and thus are effective for providing occupant crash protection in motor vehicles and the like.
While these multi-layered composite panels are very suitable and effective for achieving their intended purposes, it is desirable to provide a composite panel having all the environmental advantages, even better impact energy absorption characteristics, and an even simpler structure especially including a foam core, that may be produced by a relatively simple process.